Emission electron microscope

ABSTRACT

The invention relates to an emission electron microscope, comprising an objective lens, an imaging system with at least one lens and a stigmator. The invention is characterized in that said microscope comprises a second, independent imaging system (K 2 ), parallel to the first imaging system (K 1 ) and two electron detector devices ( 25 ) and ( 27 ), by means of which two independent images are recorded: a real image and an image of the angle distribution of the electrons as a result of electronically switching the potentials of the deflector elements ( 13 ) and ( 17 ). Both identical deflector elements comprise pairs of spherical and concentric electrodes and are electron-optically separated from each other ( 13   a ), ( 13   b ) and ( 17   a ), ( 17   b ) by double the focal length thereof and turn the electron beam through an angle corresponding to (β) and (−β), which leads to a parallel shift of the electron beam. The electrode ( 13   b ) contains a passage ( 13   c ), which allows the electron drift along the electron-optical main axis ( 29   a ), whilst the deflection is switched off. Said emission electron microscope also comprises an electron source ( 8 ), arranged close to the electron-optical axis ( 29 ) of the objective lens, which emits primary electrons along the electron-optical axis ( 28 ) at an angle (α) to the electron-optical axis ( 29 ) of the objective lens, a contrast diaphragm system ( 4   a ) in a plane correlated to the focal plane of the objective and an image diaphragm system ( 11 ), in one of the image planes of the system.

[0001] The subject matter of the invention is an emission electron microscope for the imaging of the surfaces and the angle distribution of the electrons emitted from the surface.

[0002] The system of the electrostatic lenses, known from U.S. Pat. No. 4,096,386, is characterized in that one of the lenses, e.g. the first, has a polished, flat electrode that deflects the light into the direction of the surface.

[0003] Also known from German patent application DE 198 9003 is an electron optical, imaging photo electron microscope that contains an electrostatic lens system and an image converter, the attribute of which is the suppression or retardation of the electrons.

[0004] An instrument and method of calibrating the same for the object imaging are known from U.S. Pat. No. 6,011,262, which is characterized in that the instrument contains a number of apertured diaphragms for the selective generation of the electron optical images. The instrument is also equipped with a Wien filter that enables the illumination with an electron beam.

[0005] The emission electron microscope, which comprises an objective lens having a contrast diaphragm system, a stigmator, and an electron optical imaging system having at least one lens, is additionally provided with a second, independent imaging system that is parallel to the first imaging system, and two electron detectors for the independent receipt of two images: the real image and the image of the angle distribution of the electrons, which is possible by the electronic switching of the potentials of the two deflection elements, which deflect the electron beam about an angle β and −β, and are electron optically separated from one another by double their focal length, whereby each deflection element is comprised of two spherical and concentric electrodes, of which the outermost one has a bore in order to enable the drift of the electrons along the electron optical axis with the deflection being switched off.

[0006] The emission electron microscope is also provided with: a localized electron source that is disposed closely adjacent to the electron optical axis of the objective lens and emits the electrons at an angle a to the axis of the objective lens, a contrast diaphragm system in one of the planes that is conjugated to the focal plane of the objective lens, and an image diaphragm system in one of the image planes of the emission electron microscope.

[0007] The emission electron microscope is provided in an electron suppressing or retarding system that comprises at least one electrode that simulates a spherical, suppressing central field having a center in the focal point of the objective lens.

[0008] The electron source can also become the source for the spin-polarized electrons. In the further embodiment of the emission electron microscope, the deflection system is provided with an electron detector that is disposed after the bore in the outer deflection electrode of the second deflection element and serves for the receipt of the energy spectrum.

[0009] In the further variant of the emission electron microscope, which comprises: objective lens, contrast diaphragm system, stigamator, and an imaging system having at least one lens, the emission electron microscope is provided not only with a localized electron source that is disposed closely adjacent to the electron optical axis of the objective lens, and that emits the electrons at the angle a to the axis of the objective lens, as well as a contrast diaphragm system in one of the planes conjugated to the focal plane of the objective lens, and an image diaphragm system in one of the image planes of the system.

[0010] The electron suppression or retardation system comprises at least one electrode that simulates a spherical and suppressing central field with the center in the focal point of the objective lens, and in one of the planes correlated to the focal plane of the objective lens there is disposed a contrast diaphragm system.

[0011] In the further embodiment, the electron source or the source of the spin-polarized electrons is provided with a deflection.

[0012] Coupled with the objective lens of the emission electron microscope, in a mechanical manner, is a piezoquartz driven specimen manipulator that enables the shifting, cooling and heating of the specimen.

[0013] An advantageous result of the invention is provided by: the characteristic of the imaging of the specimen surface with electrons from the selected energy range, the possibility of the local measurements of the energy spectrum and the angle distribution of the electrons, the possibility of the simultaneous receipt of the real image and an image of the angle distribution of the electrons correlated thereto. The production of this effect is realized by the use of an electronic optical deflection system that displaces the electron beam in a parallel manner, and the insertion of the electron gun into the system.

[0014] Exemplary embodiments of the invention will be described in greater detail in conjunction with the drawings:

[0015]FIG. 1 illustrates an emission electron microscope having two parallel imaging systems, an electron source, and an electron suppression or retardation system,

[0016]FIG. 2 illustrates an emission electron microscope having two parallel imaging systems and an electron source,

[0017]FIG. 3 illustrates an emission electron microscope having an imaging system and an electron source, and

[0018]FIG. 4 illustrates an emission electron microscope having an imaging system, electron source, and an electron suppression or retardation system.

[0019] The emission electron microscope illustrated in FIG. 1 comprises: an objective lens 1 with a specimen manipulator 3 and containing the contrast apertured diaphragm system 4 and stigmator 6, electron optical lenses 20, 21, 22, 23 in the imaging systems K1 and K2, electron optical lenses 10, 12, electron source 8 with deflection elements 9, and the electron optical deflection system 13 and 17 that displaces the electron beam in a parallel manner and energetically analyzes it. The system that displaces the electron beam in a parallel manner comprises: concentric deflection electrodes 13 a, 13 b and concentric deflection electrodes 17 a, 17 b, that are identical thereto and that assume the shape of partial spheres, a lens 15, stigmator 16, and electron detector 19. The first deflection element 13 deflects the electron beam about an angle β that is less than 90°, and the second deflection element 17 deflects the electron beam about an angle-β that leads to its parallel displacement. At the edges of the deflection elements 13 and 17 the annular electrodes 14 can be installed that simulate a spherical field produced by the deflection elements. Both deflection elements 13 and 17 are electron optically spaced from one another by double their focal length, and form an electron optical system in the center of symmetry of which is disposed an electron optical lens 15. Parallel displacement of an electron optical axis 29, 30 at the input and output of the system enables the observation of the microscopic image in two imaging systems K1 and K2. With a specific setting of lens 10 and the deflection element 13 switched off, via the bore 13 c in the outer electrode 13 b of the deflection element, electrons pass into the imaging system K1, where in the case of the single crystalline specimen 2 it generates a diffraction image, and in the case of the polycrystalline specimen it generates an image of the angle distribution of the electrons, whereby after the appropriate alteration of the setting of the lenses, a real image of the surface results.

[0020] With the deflection elements 13 and 17 switched on, the electron beam is subjected to a dual deflection, i.e. parallel displacement of the electron optical axis, and is thereby conveyed into the imaging system K2, which leads to the energetic selective imaging of the specimen surface with the electron detector 25.

[0021] The alternating switching on and off of the electron optical deflection elements 13 and 17 at specific voltages with a switching period shorter than the intensity drop of the two electron detectors 25, 27 leads to the detectors simultaneously showing two images:

[0022] 1) a real image that is energetically filtered by the adjustment of the deflection element 13 and of the lens 15, and an image of the angle distribution of the electrons (a diffraction image), or

[0023] 2) a real image that is energetically filtered by the adjustment of the deflection element 13 and of the lens 15, and a real image produced by all emitted electrons.

[0024] Disposed in the interior of the objective lens I is a piezoelectrical mechanism of the contrast diaphragms 4 and stigmator 6, which corrects the image errors of the objective lens.

[0025] The suppression or retardation system 7, which comprises a single or several electrodes, and that simulates a spherical central field with a center in the focal point (or in a point electron optically correlated therewith) of the objective lens 1, enables the improvement of the energy scattering capacity of the deflection element 13 via the reduction of drift energy of the electrons in the emission electron microscope.

[0026] The electron optical lens 12, the center of which is disposed in the focal plane of the deflection element 13, serves as a field lens that as a function of the operating mode of the emission electron microscope transfers either the diffraction image or the real image into the center of the electron optical lens 15. As a result of the reduction of the image plane 11, it is possible to select a fragment of the image field (even less than 1μ) and with the aid of an electron detector 19 to measure the energy spectrum of this selected field (in this case, the deflection element 13 is switched on and 17 is switched off), or with the aid of the electron optical imaging system K1 (in this case the deflection element 13 is switched off) to measure the angle distribution of the electrons from the selected field.

[0027] With the deflection element 17 switched off, the electrons drift to the electron detector 19 through the bore 17 c in the outer electrode of the deflection element 17 b.

[0028] With the deflection element 13 switched off, the electrons form a diffraction image or (as a function of the settings of the lenses 10 and 12) a real image (to which all electrons contribute) at the input of the lens 20, which after the enlargement appears upon the electron detector 27.

[0029] The switching over of the potentials with the period of e.g. 100 ms leads to the alternating appearance of the images: an energetically selective real image upon the electron detector 25, and an image of the angle distribution of the electrons (or real image to which all electrons contribute) upon the electron detector 27. Utilization of the electronic closure of the two CCD cameras, synchronized e.g. with a control signal having the period e.g. 100 ms, allows the effect of the pulsation of the simultaneously and adjacently appearing images to be avoided.

[0030] The primary electron beam passes to the specimen 2 out of the electron source 8, which is disposed closely adjacent to the electron optical axis of the objective lens. Primary electrons that enter into the region of the objective lens at an angle a to the axis thereof, and as a consequence of the application of the objective field to the point of intersection of the objective axis with the specimen are deflected, irradiate or illuminate the specimen at an angle greater than a.

[0031] The spherical or cylindrical defection electrodes 9 can be provided at the output of the electron source 8, which reduces the spacing between the electron optical axis 28 of the primary beam and the electron optical axis 29 of the objective lens, and consequently leads to the reduction of the angle of incidence of the electrons on the specimen 2.

[0032] Provided in one of the image planes of the system, e.g. in the focal plane of the deflection element 13, is an image apertured diaphragm system 11 with which it is possible to select a fragment of the image portion (also less than 1 μm) and, with the aid of an electron detector 27 or with some other independent measuring system, e.g. deflection element 13 and electron detector 19, to measure the energy spectrum of the selected portion, or with the aid of the electron optical imaging system K1 to measure the angle distribution of the electrons from the selected portion. A contrast apertured diaphragm (4 a) is provided in one of the planes conjugated to the focal plane 5 of the objective lens (e.g. in the center of symmetry of the deflection elements and 17).

[0033] The emission electron microscope of FIG. 4 is additionally equipped with a suppression or retardation system 7 that comprises one or more electrodes that simulate a spherical central field with a center in the focal point of the objective lens.

[0034] Mechanically coupled to the objective lens of the emission electron microscope is a peizoquartz specimen manipulator that enables a precise displacement, cooling and heating of the specimen.

[0035] The emission electron microscope is conceived for use under ultra high vacuum conditions, for which reason all flanges and outer dimensions are subjected to the standard CF. The base flange of the emission electron microscope is an 8″ flange DN150CF, which is provided with six mini CF flanges having electrical ducts in two parallel conduits having 2¾″ flanges. The overall instrument is covered with a magnetic shielding that protects the slow electrons in the region of the electron optical lenses from the negative influence of the external fields. 

1. Emission electron microscope that forms an electron optical lens system comprised of an objective lens, an imaging system, having at least one lens, and a stigmator, characterized in that it has a second, independent imaging system K2 that is parallel to the first imaging system K1, and two electron detectors (25) and (27) via which two independent images are detected: a real image and an image of the angle distribution of the electrons as a consequence of the electronic switching of the potentials of the deflection elements (13) and (17) that appropriately deflect the electron beam about an angle (β) and (−β), whereby the deflection elements, which are electron optically separated from one another by double their focal length, comprise identical pairs of spherical and concentric electrodes (13 a), (13 b) and (17 a), (17 b), and the electrode (13 b) contains a bore (13 c) that enables the drift of the electrons along the electron optical main axis (29 a) with the deflection switched off; in addition, the emission electron microscope also has an electron source (8) disposed closely adjacent to the electron optical axis (29) of the objective lens (1) that emits the primary electrons along the electron optical axis (28) of the electron source at an angle a to the electron optical axis (29) of the objective lens, a contrast diaphragm system (4 a) in one of the planes correlated to the focal plane (5) of the objective lens, and an image diaphragm system (11) in one of the image planes of the system.
 2. Emission electron microscope according to claim 1, characterized in that disposed in the imaging system is a suppression or retardation system (7) that comprises one or more electrodes that simulate the suppressing or retarding spherical central field with the center in the focal point of the objective lens.
 3. Emission electron microscope according to one of the claims 1 or 2, characterized in that the electron source (8) is a source of spin-polarized electrons.
 4. Emission electron microscope according to claim 3, characterized in that a deflection element (9) is disposed at the output of the electron source for the electrons.
 5. Emission electron microscope according to one of the claims 1 or 2, characterized in that a deflection element (9) is disposed at the output of the electron source (8).
 6. Emission electron microscope according to one of the claims 1 or 2, characterized in that at the electronic optical axis (18), after the bore in (17 c) the outer deflection electrode (17 b) of the deflection element (17), there is disposed an electron detector (19) for the measurement of the energy spectrum of the emitted electrons.
 7. Emission electron microscope according to claim 3, characterized in that at the electronic optical axis (18), after the bore (17 c) n the outer deflection electrode (17 b) of the deflection element (17), there is disposed an electron detector (19) for the measurement of the energy spectrum of the emitted electrons.
 8. Emission electron microscope according to claim 4, characterized in that at the electronic optical axis (18), after the bore (17 c) in the outer deflection electrode (17 b) of the deflection element (17), there is disposed an electron detector (19) for the measurement of the energy spectrum of the emitted electrons.
 9. Emission electron microscope according to claim 5, characterized in that at the electronic optical axis (18), after the bore (17 c) in the outer deflection electrode (17 b) of the deflection element (17), there is disposed an electron detector (19) for the measurement of the energy spectrum of the emitted electrons.
 10. Emission electron microscope having an electron optical imaging system that is provided with an objective lens, at least one projection lens, a stigmator, an electron detector, and a contrast diaphragm system, characterized in that disposed closely adjacent to the electron optical axis (29) of the objective lens (1) is an electron source (8) that emits primary electrons along the electron optical axis (28) at an angle a to the electron optical axis (29) of the objective lens, and in that the emission electron microscope has a contrast diaphragm system in one of the planes correlated to the focal point (25) of the objective lens, and an image diaphragm system (11) in one of the image planes of the system.
 11. Emission electron microscope according to claim 10, characterized in that in the imaging system is disposed a system (7) that suppresses or retards the electrons and that is comprised of one or more electrons that simulate a suppressing or retarding spherical central field having a center in the focal point of the objective lens.
 12. Emission electron microscope according to one of the claims 10 or 11, characterized in that a contrast diaphragm system is disposed in one of the planes electron optically conjugated to the focal plane of the objective lens.
 13. Emission electron microscope according to one of the claims 10 or 11, characterized in that the electron source (8) is a source of the spin-polarized electrons.
 14. Emission electron microscope according to claim 12, characterized in that the electron source (8) is a source of the spin-polarized electrons.
 15. Emission electron microscope according to claim 13, characterized in that the electron source (8) has a deflection element (9).
 16. Emission electron microscope according to claim 14, characterized in that the electron source of the spin-polarized electrons has a deflection element (9).
 17. Emission electron microscope according to one of the claims 10 or 11, characterized in that the electron source (8) has a deflection element (9).
 18. Emission electron microscope according to claim 12, characterized in that the electron source (8) has a deflection element (9). 